Besides angular position measuring units, which make possible an angular position measurement at a rotatable shaft in incrementable measuring steps, so-called absolute angular position measuring instruments, also referred to as rotary encoders, are conventional. These allow an absolute angle determination within a single shaft rotation. Furthermore, if the number of performed shaft rotations must be detected as well, so-called multiturn rotary encoders may be utilized. With such multi-turn rotary encoders, the absolute angular position is determined within one shaft rotation, i.e., between 0° and 360°, via a code disk connected to the shaft, which is scanned with the aid of a suitable scanning unit. In this context, a photoelectric principle may be used, but one may also use, for example, a magnetic scanning system. To obtain the required information regarding the number of shaft rotations carried out, a reduction gear may be provided, by which, given a rotating shaft, the one or more additional partial disks or encoder disks is/are set into a rotary motion at a low number of revolutions per unit time. These code disks may be designed as magnetized disks, which each have at least one north-pole sector and one south-pole sector. The rotational position of these additional code disks may be recorded with the aid of suitable scanning units, e.g., Hall sensors, in a conventional manner. Due to the predefined speed reduction of the rotary motion of the additional code disks, it is possible to record the number of effected revolutions of the shaft. Thus, the absolute position of the driven shaft may also be measured over a plurality of rotations.
A correspondingly configured multiturn rotary encoder is described, for example, German Published Patent Application No. 198 20 014 of the Assignee hereof.
The reduction gearing required in such multiturn transducers have to be largely free of play, in order to ensure a precise recording of the shaft rotations. Consequently, great mechanical requirements come about for the gear system of a multiturn transducer.
In European Published Patent Application No. 0 201 730 a gear system is described in which teeth or so-called pins revolve with the driven shaft. The revolving teeth transmit the angular momentum introduced by the drive shaft. In this context, the teeth arranged over the entire circumference of the drive shaft engage between so-called needles. This method of construction may be unfavorable, to the extent that, on the one hand, a great many movable teeth must be provided, and, on the other hand, a comparatively large space is required.
According to U.S. Pat. No. 4,715,247, a gear system type of construction is provided in which, because of a cam, a deformation of a toothed wheel is caused, so that in certain regions of the toothed wheel, engagement with an internal geared wheel takes place. For use as a reduction gear system in rotary transducers, this design may have the disadvantage that a comparatively large space is required.
There is believed to be a constant demand for rotary transducers having smaller structural dimensions. Since the electronic components of rotary transducers are being miniaturized more and more, it may be necessary that the space taken up by the mechanical components of these units be reduced too, in order to satisfy these demands with respect to size.